The present invention relates to satellites, and more particularly to a controller and control method for use in performing satellite orbit-keeping maneuvers.
Orbit-keeping is required of virtually all useful satellite applications. Orbit-keeping is typically performed by initiating a series of thruster pulses. Although ground-based operators have conventionally uplinked a command that controls a thruster pulse duration specified by orbit-keeping requirements, the pulse duration has not been automatically proportioned on the satellite to minimize the disturbance torque and also to dump any residual momentum, typically stored in spinning wheels.
Regarding generally related prior art patents, U.S. Pat. No. 5,400,252 teaches east-west orbit control during north-south maneuvers such that attitude disturbance is minimized. U.S. Pat. No. 5,349,532 teaches momentum control via ginballing and throttling during north-south maneuvers. U.S. Pat. No. 4,537,375 issued to Chan teaches ground-based thruster pulse selection (using a human operator) to minimize disturbances.
Accordingly, it would be advantageous to have an improved controller and control method for use in performing satellite orbit-keeping maneuvers. It would be advantageous to have an improved controller-and control method that automatically proportions the pulse duration on the satellite to minimize the disturbance torque and also dump residual momentum, such as is stored in spinning wheels.
The present invention provides for a controller and control method that perform satellite orbit-keeping maneuvers and that allow orbit-keeping pulses to be scaled proportionally to minimize disturbance torques automatically on-board a satellite. The controller and control method may also be used to change the momentum stored in spinning wheels, which includes both the addition or removal of momentum.
Orbit-keeping pulses vary from day to day and season to season. Prior to the present invention, each participating thruster was manually scaled proportionally to its unique disturbance using a ground-based human operator. The present invention automatically performs the proportional scaling on-board the satellite.
Exemplary apparatus in accordance with the present invention is used on a satellite having a body, a plurality of thrusters disposed on predetermined faces thereof that are used to maneuver the satellite, and a plurality of spinning momentum wheels that are used to control momentum. The apparatus comprises a controller containing a look-up table that contains data that defines which of the thrusters, and in which proportion, are to be used to perform a specified maneuver. The controller controls the plurality of thrusters to produce orbit-keeping xcex94v burns that change the orbit of the satellite and thus control satellite orbit-keeping maneuvers. The look-up table contains the time of each maneuver, the duration of each maneuver, and the direction of each maneuver.
The controller controls the thrusters to produce orbit-keeping pulses that are scaled proportionally to minimize disturbance torques on-board the satellite. The controller may also be used to control the thrusters to produce orbit-keeping xcex94v burns that remove residual momentum stored in spinning momentum wheels. The controller preferably controls the thruster on-times for the orbit-keeping pulses to create a small amount of torque to dump momentum, while keeping the overall combined thruster on-times constant. The controller processes a commandable parameter uplinked from a ground station that sets a lower limit of the quantity of momentum that is to be dumped.
An exemplary control method comprises the following steps. A satellite having a body configured with a plurality of thrusters disposed on predetermined faces thereof, a plurality of spinning momentum wheels, and a controller having a look-up table that contains data that defines which of the thrusters, and in which proportion, are to be used to perform a specified maneuver. The satellite is launched into orbit around a body, such as the earth. The plurality of thrusters are controlled using the controller to, produce orbit-keeping , xcex94v bums that change the orbit of the satellite and thus control satellite orbit-keeping maneuvers. The plurality of thrusters may also be controlled using the controller to remove residual momentum stored in the spinning momentum wheels. The controller controls the thruster on-times for the orbit-keeping pulses to create a small amount of torque to dump momentum, while keeping the overall combined thruster on-times constant. The controller processes 5 a commandable parameter that is uplinked from a ground station that sets a lower limit of the quantity of momentum that is to be dumped.
Using the present invention, an operator commands a pulse duration as specified by orbit-keeping requirements for the satellite. The pulse duration is automatically proportioned on the satellite to minimize the disturbance torque and also to dump any residual momentum. typically stored in the spinning wheels.